Rising seas and climate change: Everything you need to know

In a Globe and Mail series, Matthew McClearn examines how Canada’s most vulnerable coastal communities are preparing for potential catastrophe on their future shores. Here’s a primer on the science behind it

Oceans rose and fell hundreds of metres over many millenniums. How is our current situation different?

While it is true that sea levels have shifted radically over geologic time, they have actually been relatively stable in most places for the past 5,000 years. U.S. oceanographer John Englander, who spent the past decade raising awareness about rising sea levels, said humanity enjoyed this stability because the Earth’s climate was transitioning from a warming period to a cooling period.

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That era is over. Tide gauges (and more recently, satellite observations) reveal that the world’s oceans have risen gradually since the mid-19th century. “The records show that sea level rose over the 20th century, between one and two millimetres per year,” said Thomas James, a research scientist at Geological Survey of Canada, which is part of Natural Resources Canada. “But in the last two, two-and-a-half decades, sea level has been rising at more than double that. It’s now in excess of three millimetres per year.” This acceleration is expected to continue, translating into seas changing at rates not observed in millenniums.

Coastal communities were built with the assumption that ocean levels would remain static. That has turned out to be incorrect, and people will have to adapt in the decades and centuries ahead.

For planning purposes, many Canadian coastal communities now assume sea levels will rise one metre by the end of this century. Mr. Englander believes two, even three metres is likely. “What would three metres of sea level rise mean?” he said in an interview conducted recently as he was strolling around Vancouver. “Well, it would mean everything in front of me would be flooded. And it’s not just Vancouver, it’s every coastal community on the planet, 10,000 communities. Places we can’t even name. It’s so profound it’s hard to get our minds around.”

Coastal sensitivity

to climate change

Low

Tuktoyaktuk

Medium

High

YT

NT

Îles-de-la-

Madeleine

NU

BC

AB

NL

SK

QC

MB

ON

Vancouver

Sackville, N.B.

MURAT YUKSELIR /

THE GLOBE AND MAIL

SOURCE: CANCOAST

Halifax, N.S.

Coastal sensitivity

to climate change

Tuktoyaktuk

Low

Medium

High

Yukon

NWT

Îles-de-la-

Madeleine

Nunavut

B.C.

Alta.

Nfld.

Sask.

Que.

Man.

Ont.

Vancouver

Sackville, N.B.

MURAT YUKSELIR /

THE GLOBE AND MAIL

SOURCE: CANCOAST

Halifax, N.S.

Coastal sensitivity

to climate change

Tuktoyaktuk

Low

Medium

High

Yukon

NWT

Nunavut

Îles-de-la-

Madeleine

B.C.

Alta.

Nfld.

Sask.

Que.

Man.

Ont.

Vancouver

Sackville,

N.B.

Halifax,

N.S.

MURAT YUKSELIR /

THE GLOBE AND MAIL

SOURCE: CANCOAST

Why are the world’s oceans rising?

Primarily because the Earth’s atmosphere and oceans are warming. Mr. Englander said that, had the Earth’s natural processes prevailed, a gradual cooling would already have begun. “The problem is that with greenhouse gases, we’ve warmed the planet,” he said. “It’s a degree warmer.” Water molecules expand as they absorb heat. Referred to as “thermal expansion” or the “steric effect,” it is responsible for approximately half the sea-level rise experienced during the past 150 years.

The warming atmosphere also melted glaciers. Richard Thomson, a research scientist with the Department of Fisheries and Oceans, recalled that people could hike up to glaciers in Whistler, B.C., 30 years ago. “Those glaciers are gone now,” he said. The same thing happened in the Patagonia region of South America, the Gulf of Alaska, and across the Canadian High Arctic such as Baffin Island during the 20th century. “That water has now gone into the ocean.” Since the 1990s, rapid melting of the world’s largest ice sheets in Greenland and Antarctica contributed more water.

Benjamin Horton, a professor at Rutgers University who has specialized in sea-level change for more than two decades, has studied ocean levels over recorded human history and beyond. Dr. Horton has attributed more than half the sea-level change observed during the 20th century to human activity.

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Global emissions from fossil fuels and cement extraction

3.2 –

5.4°C

100 gigatons of CO2

Warming

relative to

1850-1900

80

60

2.0 –

3.7°C

40

2014 estimate

20

1.7 –

3.2°C

0.9 –

2.3°C

0

-20

1860

1900

1940

1980

2020

2060

2100

TRISH McALASTER / THE GLOBE AND MAIL

SOURCES: CDIAC/GCP/FRIEDLINGSTEIN ET AL 2014,

VIA GLOBAL CARBON PROJECT

Global emissions from fossil fuels and cement extraction

3.2 –

5.4°C

100 gigatons of CO2

Warming

relative to

1850-1900

80

60

2.0 –

3.7°C

40

2014 estimate

20

1.7 –

3.2°C

0.9 –

2.3°C

0

-20

1860

1900

1940

1980

2020

2060

2100

TRISH McALASTER / THE GLOBE AND MAIL

SOURCES: CDIAC/GCP/FRIEDLINGSTEIN ET AL 2014,

VIA GLOBAL CARBON PROJECT

Global emissions from fossil fuels and cement extraction

3.2 –

5.4°C

100 gigatons of CO2

Warming

relative to

1850-1900

80

60

2.0 –

3.7°C

40

2014 estimate

20

1.7 –

3.2°C

0.9 –

2.3°C

0

-20

1860

1900

1940

1980

2020

2060

2100

TRISH McALASTER / THE GLOBE AND MAIL, SOURCES: CDIAC/GCP/

FRIEDLINGSTEIN ET AL 2014,VIA GLOBAL CARBON PROJECT

How high will oceans rise this century?

We don’t know. Most models for sea-level rise are relatively consistent from now until about 2050, predicting about 20 centimetres. After that, forecasts diverge considerably.

The Intergovernmental Panel on Climate Change (IPCC), an international body set up in the late 1980s to provide regular assessments on the scientific basis for climate change, has published five assessment reports (the most recent in 2013) and is working on as ixth. With each revision, predicted sea-level rise has tended to increase. In the most extreme scenario from 2013, global mean sea-level is projected to rise by between half a metre and one metre by 2100. “It does appear to be what we’re tracking,” said Don Lemmen, a veteran of Natural Resources Canada’s climate-change division. “We are not being very successful at limiting emissions.”

The IPCC’s forecasts consider only phenomena that can be modelled with a high degree of confidence. In his book High Tide on Main Street, Mr. Englander said this approach “creates an extremely high bar or filter for what can be included. As a result a lot of very good and alarming information is almost ignored.” Forecasts from less conservative bodies – such as the U.S.National Oceanic and Atmospheric Administration (NOAA) – have predicted one metre or more of sea-level rise by 2100, with extreme scenarios reaching two or more metres.

This much is uncontroversial: Most forecasts show sea level will increase ever more rapidly as the century progresses.

Red regions represent the highest temperature increases in Antarctica over the past 50 years, with dark blue regions seeing a lesser degree of warming. The breakup of the continent’s western ice sheet will raise the seas even more – the question is when, and how much.

NASA/GSFC SCIENTIFIC VISUALIZATION STUDIO/The New York Times

Why do sea level predictions vary so widely?

There are two main sources of uncertainty, the first being that we don’t know what people will do. Most models contemplate a variety of possible national government responses to climate change, ranging from aggressive emissions reductions to no measures. “The less successful we are at reducing greenhouse-gas emissions, the greater warming there is, the greater sea-level rise we will experience,” Mr. Lemmen said.

Second, we don’t know how ice sheets will respond to the warming climate. The Greenland and Antarctic ice sheets “if not already, are shortly going to be the main sources of water into the world’s oceans,” Dr. James said. We can estimate with considerable confidence how much ice they contain: A total meltdown of Greenland’s ice sheets would raise the world’s seas more than seven metres; Antarctica would give us an additional 56 metres. “On our current warming trend, all the glaciers and ice sheets will eventually melt,” Mr. Englander wrote, “bringing us back to a planetary state that has not existed for over 30 million years.”

Virtually nobody thinks that will happen in this century, or the next. But considerable gaps remain in scientists’ understanding of how ice sheets deteriorate. For instance, lakes and rivers formed by meltwater atop Greenland’s glaciers eventually drain into sinkholes called “moulins.” Some models effectively assumed all that water goes directly into the oceans. But recently published research from the geography department of the University of California, Los Angeles, determined some becomes trapped on top of the glacier in porous, “rotten ice.” Differing predictions about how quickly ice sheets will melt result in models that differ by tens of centimetres by the end of the century.

Combined, these uncertainties explain most of the variance between models. “We cannot be certain of the outcome, regardless of what numerical models tell us,” Mr. Thomson wrote in an e-mail.

One final consideration is that not all forecasts were prepared for the same purpose. The IPCC produces highly conservative reports intended to help governments develop climate policy, and its estimates of sea level rise tend to be among the lowest. In early 2017, NOAA published an "extreme" and widely cited forecast of 2.5 metres by 2100, which was directed at risk-averse decision-makers such as operators or regulators of a seaside nuclear power plant.

May 21, 2005: A satellite image shows sea ice on Hudson Bay breaking up and slowly receding as the warmer temperatures of spring and summer make their way north into Quebec. The depression around Hudson Bay was where heavy ice during the last ice age, 18,000 years ago, pushed the earth down. Now, much of the Hudson Bay coastline is rising.

Jeff Schmaltz

Why do sea-level projections vary by community?

Counterintuitive though it may seem, communities experience sea-level rise differently. “If, hypothetically, you were to melt Greenland tomorrow, sea-level rise would not increase uniformly throughout the globe,” explained Robert Barnett, a postdoctoral research fellow at the University of Exeter who studies sea-level change. One reason is that the Earth’s crust is also constantly moving – a phenomenon known as “vertical land motion.” The introduction of Global Positioning System (GPS) stations across Canada during the early 1990s allowed researchers to measure these movements precisely.

Dr. James, a solid-earth geophysicist, studies how large ice sheets affect our planet. During the apogee of the last ice age, about 18,000 years ago, parts of central Canada lay under ice as much as three kilometres thick. “Underneath the ice, deep in the mantle, the rock actually flowed downwards and outwards,” he explained. The Earth’s surface sagged under the weight of all that ice, which forced molten rock within the Earth’s mantle downward and outward. The resulting depression was greatest where the ice was thickest – around Hudson Bay. Meanwhile, all that displaced molten rock caused areas on the periphery of the ice sheets to rise.

This process reversed once the ice sheets melted and retreated. Today, much of the Arctic coastline is rising; parts of Hudson Bay’s coastline rebound up to 15 millimetres each year. (Sea level in Churchill, Man., has consequently fallen at a rate of about one metre a century.) But “when we get out to areas like Halifax, Vancouver or Tuktoyaktuk, the land is slowly submerging,” Mr. Lemmen said. Parts of Nova Scotia’s east coast are sinking at up to two millimetres per year, resulting in sea-level rise larger than the global average.

Other forces also produce vertical land motion. Along the western coast of Vancouver Island, for example, “we have the Pacific Plate subducting underneath the North American plate,” Mr. Thomson explained. “That causes the frontal part of North America off the B.C. coast – Vancouver Island down through Oregon, Washington and California – to lift up.” Human activity such as extraction of oil, natural gas or water can cause land to sink.

Sea levels also vary regionally due to winds, air pressure, ocean currents and other natural forces, all of which can change both episodically and over the long term. For example, the Atlantic Meridional Overturning Circulation (a system of currents that includes the Gulf Stream) actually lowers water levels along the Atlantic Coast. The variation known as the El Nino Southern Oscillation, meanwhile, can have dramatic impact on sea levels along the Pacific Coast.

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How long will sea level continue to rise?

It is almost certain to go on for the remainder of your lifetime, and for generations to come. Even if humanity manages a significant reduction in greenhouse gas emissions, the oceans have already absorbed plenty of heat. The IPCC’s latest assessment predicted sea-level rise will continue for centuries, although the magnitude will depend on future emissions of greenhouse gases.

“Regardless if we go 100 per cent solar or not, we’re still going to have metres of sea level rise,” said Mr. Englander, who predicted the changes cannot be reversed for at least 1,000 years.

Even the most alarming forecasts show less than one metre of sea level rise during my lifetime. Why should I care?

The main reason is that even modest increases in sea level greatly increase the likelihood of damage from storms. “Sea level is experienced in extreme events,” said Donald Forbes, a research scientist with the Geological Survey of Canada who has studied coastal impacts of climate change across Canada. “And so, it’s not just the mean sea level creeping up. It’s the extreme events riding on that that cause flooding.” And it’s flooding that can destroy homes, ruin farmland, cause massive erosion and drown people.

Sea level responds to low pressure systems associated with storms – during powerful typhoons and hurricanes, it can rise as much as one metre. Strong winds can displace huge volumes of water, causing them to pile up against a coast, raising sea levels by several metres. The combined result is known as storm surge.

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Scientists often attempt to calculate expected frequency of storm surges. If there’s a 10 per cent chance of a certain flood level occurring in any given year, it is known as a “10-year” or “one-in-10-year” flood; a 500-year flood is a rare but disastrous event. These are known as “return periods,” a term that often causes confusion. In any given century, a 100-year flood could happen twice, three times, or not at all.

Here’s the bad news: “A high storm surge will be higher with higher sea level,” Mr. Forbes said. “And what is today a damaging flood level, but very rare, say 1-in-100-year, with relatively moderate sea level rise, that becomes a 1-in-10, 1-in-5 or a 1-in-2-year event.” We can expect many more damaging storms similar to Hurricane Juan (which flooded much of Halifax in 2003) in the decades ahead.

0

5

KM

Dartmouth

Halifax

NOVA SCOTIA

Coastal sensitivity

to climate change

Low

Medium

High

MURAT YUKSELIR / THE GLOBE AND MAIL,

SOURCE: CANCOAST

0

5

KM

Dartmouth

Halifax

NOVA SCOTIA

Coastal sensitivity

to climate change

Low

Medium

High

MURAT YUKSELIR / THE GLOBE AND MAIL,

SOURCE: CANCOAST

0

5

KM

Dartmouth

Halifax

NOVA SCOTIA

Coastal sensitivity

to climate change

Low

Medium

High

MURAT YUKSELIR / THE GLOBE AND MAIL, SOURCE: CANCOAST

Violent hurricanes seem to be more common in recent years. Will that continue?

There’s some consensus – not just among scientists, but also among coastal communities – that warming oceans and other climate factors increase both the intensity and frequency of storms. But the evidence supporting such claims is shaky. The IPCC’s latest assessment placed “low confidence” in regional-specific projections in storminess and storm surges.

It’s even conceivable that some places will enjoy calmer weather. In one document, Nova Scotia’s provincial government acknowledged that “there is debate in the scientific community over the link between climate change and tropical storm frequency. Because these storms tend to behave in a cyclical way, it’s also possible that they will decrease in number over the next 10 to 20 years.”

Rapid meltdown of ice sheets in Greenland, Antarctica or both. James Hansen, a climate science professor at Columbia University, has argued most climate models seriously underestimate how quickly they will go. In a paper published last year, he said that owing to the complex manner in which melting ice sheets and processes in the world’s oceans affect one another, it is more likely they will melt at an exponential rate rather than the more linear pattern assumed by most models.

Dr. Hansen has claimed sea level could rise as much as five metres this century, causing the “loss of all coastal cities.” Say goodbye to Vancouver, Halifax and St. John’s. Canada’s geography would change in other important ways. According to the Nova Scotia Community College’s Applied Geomatics Research Group, portions of the Chignecto Ithmus (the land bridge joining Nova Scotia to New Brunswick) would flood completely if sea levels rose four or more metres. Nova Scotia would become an island.

And if that is not enough, Dr. Hansen warns that freshwater from melting ice spilling into the upper ocean layers is already slowing oceanic circulations inthe North Atlantic and Southern Oceans. These powerful currents could cease altogether. One result could be catastrophic superstorms on a scale not seen in tens of thousands of years. “All hell will break loose in the North Atlantic and neighbouring lands,” he predicted in one video broadcast.

Dr. Hansen’s doomsday predictions lie considerably outside mainstream climate models. But before you dismiss them, consider one caveat: Yesterday’s extreme sea-level rise forecasts have a way of becoming today’s base case. “If you look at the history of climate change modelling and prediction over the past 15 years, usually it turns out worse than the models predicted,” said David Lieske, a geography professor at Mount Allison University.

Homes on the shores of Tuktoyaktuk, one of the five communities chosen to be profiled in the Sea Change series.

Patrick Dell/The Globe and Mail

How did The Globe and Mail select the communities profiled in Sea Change?

To identify coastal communities in Canada that are highly vulnerable to rising sea levels, The Globe first turned to CanCoast, a geospatial database created by members of the Geological Survey of Canada.

CanCoast contains detailed information about the characteristics of individual segments of Canada’s coastline, including the topographical relief ofthe nearshore area, local bedrock geology, local conditions such as tidal range and wave heights. (Much of CanCoast’s underlying data and concepts have existed for at least a couple of decades, as this 1994 map from the Geological Survey of Canada makes clear.) Those characteristics were used to calculate the CanCoast Sensitivity Index (CSI),which assesses overall vulnerability to climate change.

We acquired the CanCoast data set and explored it using ArcGIS, a geographical information system software package, to identify communities with higher-than-average CSI scores. The Globe then conducted additional research and reporting to learn more about conditions and challenges these communities face.(This report from Natural Resources Canada proved particularly helpful.)

We sought at least one community from each major stretch of Canadian coastline (west, north and east). We also wanted a mixture of major cities and remote communities, and a diversity of challenges and approaches to adaptation. We selected five: Halifax, the Îles-de-la-Madeleine, Que., Sackville, N.B., Tuktoyaktuk, NWT, and Vancouver.

How bad is Canada’s plight relative to that of other countries?

Readers of Brian Fagan’s 2013 book The Attacking Ocean learn that four-fifths of Bangladesh’s territory rests on the floodplain of the sprawling delta formed by the Ganges, Meghna and Brahmaputra rivers. How many of the country’s 163 million inhabitants will be forced to relocate during this century is difficult to predict, but inevitable displacements might have dramatic implications for neighbouring countries and beyond. With an average of more than 1,200 persons per square kilometre, Bangladesh is already among the most densely populated nations on Earth.

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Shanghai, now teeming with 24 million inhabitants, established itself in recent decades as a global megacity rivaling London and New York. But a broader survey of its history reveals its vulnerability to the capricious sea and Yangtze River. The city sank more than two metres during the 20th century, in part because rapidly expanding industries pumped huge volumes of groundwater from the aquifers underneath. Much of it lies below the high-tide mark and is protected by hundreds of kilometres of dikes and other defences; buttressing them is among the few options for preventing Shanghai’s near-complete submersion in the century ahead.

No point on the tiny Polynesian archipelago nation of Tuvalu is higher than 4.6 metres above sea level; even a modest increase “could render Tuvalu uninhabitable,” Mr. Fagan wrote. Evacuation is among the few options for its 11,000 inhabitants, who have more than doubled in number since 1980. Tuvalu has no evacuation strategy – but abandonment is its only obvious long-term option.

According to a study led by World Bank economist Stephane Hallegatte, global flood losses will increase from US$6-billion a year in 2005 to as much as US$1-trillion by mid-century, assuming large coastal cities fail to adapt.

Canada is better situated than Tuvalu or Bangladesh. According to a 1998 paper published by the Geological Survey of Canada, just 3 per cent of Canada’s coastline is “highly sensitive” to sea-level rise. Large swaths of it are protected somewhat because of hard bedrock, weak wave action and other geographic and geological features. For some northern communities, such as Churchill, Man., sea-level rise could be welcomed, because the earth’s crust there is rising even more quickly.

Our sprawling coast is also largely undeveloped compared with large swaths of the United States, Europe and Japan. With the notable exception of B.C.’s LowerMainland, Canada’s largest cities lie beyond the reach of the tides. In a 2013 World Bank paper that studied flood hazards facing major coastal cities around the world, Vancouver ranked 16th by current exposure – well behind leaders like Miami, New York and Tokyo. Perhaps more significantly, it was absent from the list of 20 cities expected to experience the largest increase in annual flooding-related losses by mid-century.

Yet the misery of others in no way diminishes the challenge ahead for Canada’s coastal communities. As detailed in The Globe’s Sea Change series, for some the threat is existential.

A man sits on top of The Wave, a sculpture on the Halifax waterfront. Rising sea levels could leave the Nova Scotia capital much more vulnerable to flooding during extreme storms, like 2003’s Hurricane Juan.

Darren Calabrese/The Globe and Mail

How are they preparing?

There are essentially four main adaptation strategies. Avoidance involves preventing development in areas identified as being at risk offlooding. Protection includes erecting barriers such as dikes and seawalls – or more “natural” defences like marshes and dunes. Communities thatchoose accommodation design their buildings and infrastructure with the understanding that they will experience flooding – such as moving electrical equipment above expected flood levels, or ensuring the main floors of residential buildings have nobody living on them. And then there’s managed retreat – strategic withdrawal from areas destined to become uninhabitable or deemed not worth saving. This may include offering subsidies to encourage relocation, purchasing land, and discouraging erection of coastal defences.

Examples of all four approaches are cropping up along Canada’s coasts. But all communities we visited were still in the early stages of understanding the risks. Unsurprisingly, large cities such as Vancouver and Halifax possess the most data on the risks presented by rising sea levels and the related effects of climate change. That information is crucial to avoid maladaptation – attempts that fail to reduce risk or make matters worse.

High-resolution topographical surveys, consultants’ reports and vague plans for climate-change adaptation are no substitute for action. Vancouver and Halifax continue to develop seaside infrastructure in the absence of anything resembling a comprehensive plan to address the fact that much of it could flood regularly within a century. In rural coastal areas, Canadians continue to build luxurious seaside homes in vulnerable areas. “We’ve had a tendency over the past two decades to increase our vulnerability by increasing our exposure,” Mr. Forbes observed.

It’s difficult to know how long that will continue. Given election cycles lasting four or five years, few policy-makers are motivated to address a problem that will strike hardest an electorate that remains largely unborn. And most adaptation options are bound to be expensive. Small coastal communities like Tuktoyaktuk and Îles-de-la-Madeleine are already looking to higher levels of government to finance their adaptation efforts. But there are as yet no deep pools of disaster relief money to tap, and provinces and the federal government are already dealing with elevated debt.

Even at today’s accelerated rates, sea level rise is still imperceptible, just millimetres a year. Although a catastrophic storm surge could theoretically strike any of these communities tomorrow, odds are that they still have decades to prepare.

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